Method and apparatus for high rate channel access control

ABSTRACT

Access to a variable rate multiple access system is controlled based upon a current loading. The current loading level is used to determine a transmission rate set point. The transmission rate set point may include a maximum transmission rate and a transmission probability. The transmission rate set point is passed to the remote unit which may access the system. A remote unit with data to send determines a desired transmission data rate. If the desire transmission data rate is equal to or greater than the maximum transmission data rate, the remote unit transmits at the maximum transmission data rate with a probability equal to the transmission probability.

This application is a continuation of U.S. Pat. No. 6,567,420, issuedMay 20, 2003 entitled “Method and Apparatus for High Rate Channel AccessControl.”

BACKGROUND OF THE INVENTION

I. Field of the Invention

The invention relates to communication systems. More particularly, theinvention relates to resource allocation in a multiple access system.

II. Description of the Related Art

FIG. 1 is an exemplary embodiment of a terrestrial wirelesscommunication system 10. FIG. 1 shows three remote units 12, 13, and 15and two base stations 14. In reality, typical wireless communicationsystems may have many more remote units and base stations. In FIG. 1,the remote unit 12 is shown as a mobile telephone unit installed in acar. FIG. 1 also shows the fixed location remote unit 15 in a wirelesslocal loop system and the portable computer remote unit 13 in a standardcellular system. In the most general embodiment, the remote units may beany type of communication unit. For example, the remote units may behand-held personal communication system (PCS) units, portable data unitssuch as a personal data assistant, or fixed location data units such asmeter reading equipment. FIG. 1 shows a forward link signal 18 from thebase stations 14 to the remote units 12, 13 and 15 and reverse linksignal 19 from the remote units 12, 13 and 15 to the base stations 14.

In a typical wireless communication system, such as that illustrated inFIG. 1, some base stations have multiple sectors. A multi-sectored basestation comprises multiple independent transmit and receive antennas aswell as some independent processing circuitry. The principles discussedherein apply equally to each sector of a multi-sectored base station andto a single sectored independent base station. For the remainder of thisdescription, therefore, the term “base station” can be assumed to referto either a sector of a multi-sectored base station, a plurality ofsectors associated with a common base station or a single sectored basestation.

In a CDMA system, remote units use a common frequency bandwidth forcommunication with all base stations in the system. Use of a commonfrequency bandwidth adds flexibility and provides many advantages to thesystem. For example, use of a common frequency bandwidth enables aremote unit to simultaneously receive communication signals from morethan one base station, as well as transmit a single signal for receptionby more than one base station. The remote unit discriminates thesimultaneously received signals from the various base stations throughthe use of the spread spectrum CDMA waveform properties. Likewise, thebase station can discriminate and separately receive signals from aplurality of remote units.

In a wireless system, maximizing the capacity of the system in terms ofthe number of simultaneous calls that can be handled is extremelyimportant. System capacity in a spread spectrum system is increased ifthe power received at the base station from each remote unit iscontrolled such that each signal arrives at the base station receiver atthe minimum power level required to obtain a desired signal qualitylevel. If a signal transmitted by a remote unit arrives at the basestation receiver at a power level that is too low, the signal qualitymay fall below an acceptable level. If, on the other hand, the remoteunit signal arrives at a power level that is too high, communicationwith this particular remote unit is acceptable, but the high powersignal acts as interference to other remote units. This excessiveinterference may adversely affect communications with other remoteunits. Thus, in general, a remote unit located near the base stationtransmits a relatively low signal power while a remote unit located atthe edge of the coverage area transmits a relatively large signal power.

In more advanced systems, in addition to controlling the power level atwhich the remote unit transmits on the reverse link, the data rate atwhich the remote unit transmits on the reverse link is also controlled.A remote unit located on the edge of a coverage area may reduce the datarate at which it transmits in order to increase the signal quality ofthe signal as received at the base station. By reducing the data rate,the time devoted to each bit may be increased, thus, increasing theenergy devoted to each bit and increasing the performance of the link.

In addition to link performance, the use of variable data rates can alsoprovide other benefits to the system. For example, a remote unit maygenerate a stream of data which is being produced at a data ratesignificantly below a maximum data rate. The remote unit may chose totransmit the data at a rate lower than the maximum rate in order toconserve remote unit power and spectral resources. In addition someremote units may be categorized according to the level of service whichthey provide. For example, a preferred client remote unit may providedata transfer up to a maximum rate while an economy level remote unitmay provide data transfer at one-eighth, one-quarter or one-half of themaximum rate. A remote unit which transmits at less than the maximumrate may transmit at a lower power level or it may transmit only aportion of the time. For example a remote unit transmitting atone-quarter of the maximum rate may transmit its signal at one-quarterof the power which would be necessary to transmit a full-rate signal.Alternatively, a remote unit which is transmitting at one-quarter of amaximum rate may transmit with a duty cycle of approximately one overfour. In either case, a remote unit which transmits at less than thefull rate generates less interference and consumes less system resourcesthan a remote unit transmitting at full rate, thereby, freeing systemresources for use by other remote units.

If a minimum acceptable signal quality is specified, an upper bound onthe number of simultaneous users which can communicate through a basestation can be calculated at a given level of interference. This upperbound is commonly referred to as pole capacity. The ratio of actualusers to pole capacity is defined as the loading of the system. As thenumber of actual users approaches the pole capacity, loading approachesunity. A loading close to unity implies potentially unstable behavior ofthe system. Unstable behavior can lead to degraded performance in termsof error rate performance, failed hand-offs, and dropped connections. Inaddition, as loading approaches unity, the size of the coverage area ofthe base station shrinks such that users on the outer edge of thecoverage area may no longer be able to transmit sufficient power tocommunicate with the base station at an acceptable signal quality evenat the lowest available data rate.

For these reasons, it is advantageous to limit the usage of a systemsuch that loading does not exceed a specified percentage of the polecapacity. One way to limit the loading of the system is to deny accessto the system once the loading of the system has reached a predeterminedlevel. For example, if the loading increases above 70% of the polecapacity, it is advantageous to deny requests for additional connectionoriginations and to refrain from accepting hand-off of existingconnections. In a system in which the remote units are capable oftransmitting at multiple data rates, the loading of the system can alsobe controlled by controlling the data rate at which the remote unitstransmit. For a given level of loading, by reducing the data rate atwhich each remote unit may transmit, the total number of remote unitsable to access the system may be increased.

In a typical digital data multiple access system, a remote unitestablishes a communication session with the base station. The sessionremains active until power is removed from the remote unit or until theremote unit requests a disconnection. Once a session has beenestablished, a remote unit transmits bursts of data. For example, if aremote unit user connects to an internet via a wireless connection andhis notebook computer, he establishes a session when he logs into thenetwork. If the remote unit user generates an e-mail message, the remoteunit generates a burst of data when it transfers the e-mail message. Theburst of data may contain one or more packets of data. The packets ofdata typically comprise many wireless link frames of data.

In a system in which the data rate of the remote unit is controlled bythe base station, before the remote unit transmits a burst of data, itsends an access request message to the base station. Typically, theaccess request message specifies the desired transmission data rate. Inresponse the base station may give permission for the remote unit totransmit at the desired data rate, may give the remote unit permissionto transmit at a lower data rate, or may deny access to the system. Theuse of such a system has several drawbacks. For example, the use of anaccess request message consumes the precious reverse link resources. Inaddition, the transmission of data over the reverse link is delayedwhile the remote unit and base station negotiate a data rate. Inaddition, the algorithm which must be used by the base station torespond to the access request messages from a plurality of remote unitsis complicated and consumes considerable base station resources.

For these reasons, there has been a long felt need in the industry for amethod and apparatus for controlling access to a multiple access systememploying a variable data rate transmission scheme.

SUMMARY OF THE INVENTION

A base station is used to control the reverse link transmission ratesfor remote units within the corresponding coverage area. The basestation monitors the reverse link loading and dynamically adjusts thetransmission rate set point. The transmission rate set point may bedefined in terms of a maximum transmission rate and a transmissionprobability. The maximum transmission rate defines the maximum reverselink data rate available to the remote units. The transmissionprobability is used to control the probability that a remote unittransmits at the given maximum transmission rate. The base station maybroadcast the transmission rate set point to the remote units. Theremote units may transmit at a rate lower than the maximum transmissionrate at any time. In this way, the loading of the system is controlledin a fast and stable manner which efficiently utilizes available systemresources.

BRIEF DESCRIPTION OF THE DRAWINGS

The features, objectives, and advantages of the invention will becomemore apparent from the detailed description set forth below when takenin conjunction with the drawings:

FIG. 1 is an exemplary embodiment of a terrestrial wirelesscommunication system;

FIG. 2 is a flow chart illustrating base station operation;

FIG. 3 is a flow chart showing exemplary remote unit operation; and

FIG. 4 is a block diagram showing an exemplary wireless systemincorporating use of the invention.

DETAILED DESCRIPTION OF THE INVENTION

In a multiple access system which has finite resources, a means ofcontrolling the reverse link loading is necessary in order to avoidunstable system behavior. In a system in which the remote units arecapable of transmitting data at a plurality of data rates, the reverselink loading may be controlled by regulating the data rate at which theremote units transmit. For example, in a system in which the level ofexternal and mutual interference allow thirty remote units to access thesystem simultaneously at a given data rate, the same system may allowsixty remote units to access the system simultaneously if each of theremote units transmits at one-half of the given data rate. If a portionof the remote units transmits at one-half of the given data rate, thesystem may accommodate a number of simultaneous users between thirty andsixty. Under actual operating conditions, the capacity of a system issoft limiting meaning that each remote unit which is added to the systemreduces the signal quality at which each of the other system usersoperates. The capacity is also a function of time in that interferencefrom sources other than remote units varies over time and may contributesignificantly to the loading of the system. Because it is advantageousto avoid a catastrophic failure which may result if the loading exceedsthe maximum capacity, typically system operators limit the loading tobetween 60% and 75% of the anticipated capacity limit.

In order to limit the loading on the reverse link to a specified level,it is necessary to measure the reverse link loading. Reverse linkloading of a base station is not only a function of the remote unitsthat are operating within the coverage area of the base station. Reverselink loading is also a function of interference from other sources. Thefront end noise of the base station itself is a significant source ofinterference. In addition, other remote units operating on samefrequency within the coverage area of nearby base stations contributesignificant interference. U.S. Pat. No. 6,603,745 entitled “METHOD ANDAPPARATUS FOR REVERSE LINK OVERLOAD DETECTION”, issued Aug. 5, 2003,assigned to the assignee hereof and incorporated in its entirety herein,discloses a means and method of determining loading. A myriad of methodsof determining loading may be used in conjunction with the invention.

According to the present invention, a base station uses a measure ofloading on the reverse link in order to control the data rate at which aplurality of remote units transmit. In a typical multiple access system,the base station routinely transmits an overhead channel. The overheadchannel carries information which is received by multiple remote units.The overhead channel carries information concerning system operationsuch as the identity of nearby base stations, the availability ofcertain services and the identity of the system operator. According toone embodiment of the present invention, in addition to the standardoverhead information, the base station also transmits a transmissionrate set point. The remote unit retrieves the set point information fromthe overhead channel and uses it to determine the rate at which ittransmits.

In one embodiment, the transmission rate set point is defined in termsof a maximum transmission data rate as well as a transmissionprobability. The maximum transmission rate defines the maximum reverselink data rate for use by the remote units. The transmission probabilityis used to control the probability that a remote unit transmits at thegiven maximum transmission rate. The remote units may transmit at a ratelower than the maximum transmission rate at any time.

In order to facilitate efficient use of system resources, it isadvantageous to allow the system to operate as close as possible to thecapacity limit in view of the corresponding probability of unstablesystem behavior. According to the invention, the transmission rate setpoint is slowly increased as long as the loading of the system remainsbelow the maximum allowable loading. If the actual loading of the systemexceeds the maximum allowable loading, the transmission rate set pointis decreased.

In one embodiment, so long as the loading of the system remains thebelow the maximum allowable loading, the transmission probability isslowly increased. When the transmission probability exceeds unity, themaximum transmission data rate is increased to the next higher availablelevel and the transmission probability is reduced. In this way thetransmission rate set point slowly increases until the loading reachesthe maximum allowable loading. If the available system resources aresufficient to support the needs of all the remote units, thetransmission rate set point increases until the transmission probabilityis equal to 1 and the maximum transmission rate is equal to the highestdata rate. If the available system resources are not sufficient to alloweach remote unit to transmit at its desired rate, as the transmissionrate set point slowly increases, the loading eventually exceeds themaximum allowable loading. Once the loading exceeds the maximumallowable loading, the transmission rate set point is reduced. If thedemand remains constant, the system reaches an equilibrium where thetransmission rate set point is approximately equal to the maximumallowable transmission rate set point. For example, if the demand on thesystem is high, the maximum transmission rate may be set to one-half offull rate and the transmission probability may be less than unity.

In the preferred embodiment, the lowest possible transmission rate setpoint is defined as a maximum transmission rate equal to the lowest datarate and a transmission probability equal to 1. Therefore, even undermaximum loading conditions, each remote unit with an establishedconnection is enabled to transmit at the lowest rate with a probabilityof unity. In order to maintain system stability, it may be necessary todeny access to the system to additional remote units if the loadingexceeds the maximum allowable loading when the transmission rate setpoint is at a minimum.

One benefit of operation according to the present invention is that thetransmission control process at the base station relatively easy toimplement. Only a single input to the process is used to determine thetransmission rate set point. In one embodiment, the transmission rateset point consisting of only two numbers is the only output. Incomparison with the prior art method of individually responding tosporadic access requests messages from the various remote units eachtime the remote unit has data to transmit, the operation of theinvention is streamlined. Operation is not dependent upon inputconcerning such factors as the number of current users or theanticipated usage of the users or the quantity of remote units within acertain class. In addition, the operation does not require large amountsof data storage to store information concerning recently grantedadmissions to remote units.

FIG. 2 is a flow chart illustrating base station operation. Operationbegins at start block 30. In block 32, the variables used in the processare set to initial values. The transmission probability is set to 1 andthe maximum transmission rate is set to the lowest data rate in order toset the transmission rate set point to its minimum value. In anexemplary system, the lowest data rate may be one-eighth of the fullrate.

In block 32 the down-rate “Δ_(TP)” and the up-rate “δ_(TP)” are set to anominal level. In an exemplary system, the value of the down-rate andthe up-rate depend upon the current maximum transmission rate. Forexample, in a system in which data may be transmitted at one-eighth of afull rate, one-quarter of a full rate, one-half of a full rate, and afull rate, the value of Δ_(TP) may be one-half, one-quarter, one-eighthand one-sixteenth, respectively. In a typical environment, the value ofδ_(TP) is less than the value of Δ_(TP). For example, in this systemjust described, the value of δ_(TP) may be one-sixteenth of the value ofΔ_(TP) for each data rate.

Block 34 determines whether loading has exceeded the maximum allowableloading. If not, flow continues to block 36 where the transmissionprobability is increased by δ_(TP). Flow continues to block 38 whichdetermines whether the transmission probability has exceeded 1. In thiscase, because the transmission probability was set to 1 in block 32 andincreased by the value of δ_(TP) in block 36, the transmissionprobability has exceeded 1 and flow continues in block 40. Block 40determines whether the maximum transmission rate is equal to the highestdata rate. In this example, a maximum transmission data rate was set tothe lowest rate in block 32 and, therefore, the maximum transmissiondata rate is not equal to the highest data rate and flow continues inblock 42. In block 42 the maximum transmission rate is set to the nexthigher data rate. For example, in a system with four data rates, themaximum transmission data rate may be set to one-quarter of the fullrate. In block 44, the value of the transmission probability is reducedby 1. Flow continues to block 48 where the process may be paused inanticipation of the next cycle.

Returning again to block 38, if the transmission probability has notexceeded 1, flow continues directly to block 48. Returning to block 40,if the maximum transmission rate is already equal to the highest datarate, the transmission rate set point is at its maximum level and flowcontinues in block 46. In block 46, the transmission probability is setto 1. Flow then continues to block 48.

Returning again to block 34, if the loading has exceeded the maximumallowable loading, flow continues in block 50. In block 50, thetransmission probability is reduced by Δ_(TP) and flow continues inblock 52. Block 52 determines whether the maximum transmission rate isequal to the lowest data rate. If the maximum transmission rate is equalto the lowest data rate, flow continues in block 46 where thetransmission probability is set to 1. If the maximum transmission rateis not equal to the lowest data rate, flow continues to block 54. Block54 determines whether the transmission probability is less than or equalto zero. If so, the maximum transmission rate is set to the next lowerdata rate in block 56 and flow continues in block 58. Block 58determines whether the maximum transmission data rate is equal to thelowest data rate. If so, flow continues in block 46 where thetransmission probability is set to 1. If not, flow continues to block 60where the transmission probability is increased by 1. In either case,flow continues to block 48.

The operation within the remote unit is also simplified in comparison tothe generation of an access request message before each transmission.According to the invention, the remote unit chooses a desiredtransmission rate. A myriad of criteria and methods for determining thedesired data rate may be used in conjunction with the present invention.For example, the determination of the desired data rate may take intoconsideration the amount of data queued for transmission, the availabletransmission power which can be dedicated to higher data rates, theclass of service requested by the user, or the level of urgencyassociated with the transmission. Additional information concerning theselection of a desired data rate may be found in U.S. Pat. No. 5,914,950entitled “METHOD AND APPARATUS FOR REVERSE LINK DATA RATE SCHEDULING”issued Jun. 28, 1999, assigned to the assignee hereof. The remote unittransmits at the desired data rate so long as the desired data rate isless than the maximum transmission rate received from the base station.If the desired rate is equal to or exceeds the maximum transmissionrate, the remote unit transmits at the maximum transmission rate with aprobability equal to the transmission probability. If the remote unitdoes not transmit at the maximum transmission rate, it transmits insteadat the next lower rate. In this way, in the general case, the ratio ofthe number of users transmitting at the maximum transmission ratecompared to the number of remote units of the same class which desire totransmit at the maximum transmission rate or higher is equal to thetransmission probability on average. In this way, system resources areused efficiently and fairly.

If a remote unit is in soft hand-off with one or more base stations, itmay receive a transmission rate set point from more than one basestation. The remote unit may use the lowest transmission rate set pointreceived from any one of the base stations with which it is in softhandoff. The lowest rate set point may be determined by selecting thetransmission rate set point which specifies the lowest maximumtransmission rate or, if the maximum transmission rates are equal, thetransmission rate set point with the lowest transmission probability.Alternatively, the remote unit may use the highest rate set point or itmay average or otherwise combine the two transmission rate set points.

FIG. 3 is a flow chart showing exemplary remote unit operation. Flowbegins in start block 70. In block 72, the remote unit determines itsdesired data rate. Once the desired data rate is determined, flowcontinues in block 74. Block 74 determines if the desired data rate islower than the most recently received maximum transmission data rate. Asnoted above, the remote unit may monitor an overhead channel for thecurrent value of the transmission rate set point. If the desired datarate is lower than the maximum transmission rate, the remote unit mayset the transmission data rate to the desired data rate in block 82. Inblock 86, the system uses the just-determined transmission rate until anew value is determined. If the desired data rate exceeds or is equal tothe maximum transmission rate, flow continues from block 74 to block 76.In block 76, the remote unit generates a random number. In the preferredembodiment, the random number takes on a value between 0.00 and 0.99.Block 78 determines whether the random number is less than the mostrecently received transmission probability. If so, the transmission rateis set to the maximum transmission rate in block 80. If not, thetransmission rate is set to the next lower transmission rate down fromthe maximum transmission rate in block 84. In either case, flowcontinues to block 86.

According to the invention, the transmission of data from the remoteunit occurs at the transmission rate set in block 80, 82 or 84. In thisway, reverse link capacity is not consumed with the transmission ofaccess request messages. In addition the transmission of reverse linkdata is not delayed by the access request process.

One advantage of the present invention is that it lends flexibility tothe system administrator to control the operation of the system. Forexample, as the loading of the system is increased, the probability ofunstable system behavior also increases. Thus, the probability ofunstable system behavior is dependent upon the value of the maximumallowable loading. A system operator control the probability ofcatastrophic system outage, at the expense of average capacity, in orderto satisfy his current criteria by simply changing the maximum allowableloading value.

In addition, should the system operator wish to allow certain remoteunits to be high priority users which are permitted to transmit outsideof the constraints imposed by the transmission rate set point, he may doso without making any changes to the access control process. In such acase, the transmission rate set point of the system is lowered by thenatural operation of the process to compensate for these users. Forexample, the preferred users may access the system at either full rateor at the maximum transmission rate with a transmit probability of 1 atall times, thereby increasing the loading to the system. The inventioncompensates for that condition by lowering the transmission rate setpoint of the lower priority units and does so without any knowledge ofthe high priority user's presence in the system. In addition, the systemadministrator may control the value of Δ_(TP) and δ_(TP) in order tochange the character of the operation of the system.

FIG. 4 is a block diagram showing an exemplary wireless systemincorporating use of the invention. The system is comprised of a basestation 114 and a remote unit 100. The base station 114 may be locatedin close proximity to its corresponding coverage area or some of thecomponents within the base station 114 may be remotely located. The basestation 114 receives wireless link signals over an antenna 116. Areceiver 118 is used to convert the wireless link signal to a digitalbit stream. In addition, the receiver 118 provides an output to a loaddetermination process unit 120 which is used to determine a currentloading of the system. The output of the load determination process unit120 is passed to an access control process unit 122 which provides manyof the core functions of the invention. For example, the access controlprocess unit 122 may comprise a plurality of processes which execute thesteps exemplified in FIG. 2. The output of the access process unit 122is the transmission rate set point which is passed to a controller 126.The controller 126 may oversee the general operation of the basestation. In one embodiment, the controller 126 incorporates thetransmission rate set point into an overhead message and passes it totransmitter 124. The transmitter 124 creates a wireless link signal andpasses it to the antenna 116 for transmission over the wireless link toa plurality of remote units including the remote unit 100.

Generally, the remote unit 100 may be or may be coupled to any type ofterminal which produces digital information. For example, the remoteunit 100 may be or may be coupled to a personal notebook computer, aprinter, test equipment, a server, a dumb terminal or a variety of otherequipment. The remote unit 100 is comprised of a controller 102 whichmay oversee the operation of the remote unit 100. In the embodimentshown in FIG. 4, the controller 102 receives digital data from aseparately housed unit. The controller also receives data from areceiver 104 created from a wireless link signal received over anantenna 110. The controller 102 extracts the transmission rate set pointfrom the data received from the receiver 104 and passes it to a ratedetermination process unit 106. The rate determination process unit 106determines the current transmission rate. For example, the ratedetermination process unit 106 may have a series of processes whichperform the functions shown in FIG. 3. The current transmission rate isused by a transmitter 108 in order to transmit data over the antenna 110to the base station 114.

A myriad of alternate embodiments consistent with the present inventionwill be readily discernible to one skilled in the art. For example,referring again to FIG. 2, instead of subtracting 1 from the value ofthe transmission probability in block 44, the transmission probabilitymay be set to 0 or some small number. Likewise, instead of adding one tothe value of the transmission probability in block 60, the transmissionprobability may be set to 1 or close to unity. In the example shownabove, operation included four different data rates. A greater or fewernumber of data rates could be used consistently with the invention.Although the description herein has referred to digital data systems,the principles are directly applicable to a number of variable ratesystems including voice systems.

In the exemplary embodiment shown above, the values of Δ_(TP) and δ_(TP)are dependent upon the maximum transmission rate. In other embodimentsthey may be fixed throughout operation or they may be dependent uponsome other variable. Although use of the overhead channel lendsefficiency to the system, the transmission rate set point may becommunicated to a remote unit on a dedicated channel consistent with theinvention.

The transmission probability can take on one of a variety of forms. Inthe example above, the transmission probability reflects the probabilitythat the remote unit transmits at the maximum transmission rate.Alternatively, the transmission probability could reflect theprobability that the remote unit transmits at the next lower rate belowthe maximum transmission rate. In order to impose the restriction of thetransmission probability, the example above used random numbergeneration. A myriad of other well known and later developed schemes maybe used in order to impose the restriction.

The invention may be embodied in other specific forms without departingfrom its spirit or essential characteristics. The described embodimentis to be considered in all respects only as illustrative and notrestrictive and the scope of the invention is, therefore, indicated bythe appended claims rather than by the foregoing description. Allchanges which come within the meaning and range of equivalency of theclaims are to be embraced within their scope.

1. A method of accessing a system utilizing multiple data ratescomprising the steps of: determining a desired transmission data rate;setting a current data transmission rate to said desired transmissiondata rate if said desired rate is less than a maximum transmission rate;setting said current data transmission rate to said maximum transmissionrate with a probability equal to a transmission probability if saiddesired transmission rate exceeds or is equal to said maximumtransmission rate; and transmitting data at said current datatransmission rate.
 2. The method of claim 1 wherein said maximumtransmission rate and said transmission probability are received over abroadcast channel.
 3. The method of claim 1 further comprising the stepof setting said current data transmission rate to a data rate less thansaid maximum transmission rate with a probability equal to one minussaid transmission probability if said desired transmission rate exceedsor is equal to said maximum transmission rate.
 4. The method of claim 1further comprising the steps of: receiving a first transmission rate setpoint comprising said maximum transmission rate and said transmissionprobability from a first base station through which communication isestablished; receiving a second transmission rate set point from asecond base station through which communication is established; andusing said first transmission rate set point to determine said currentdata transmission rate if said first transmission rate set point islower than said second transmission rate set point.
 5. A multiple accesscommunication apparatus comprising: a receiver for receiving a maximumtransmission rate and a transmission probability produced by a baseunit; a rate determination process unit for determining a desiredtransmission data rate; the rate determination process unit for settinga current data transmission rate equal to said desired transmission datarate if said desired rate is less than said maximum transmission rate;the rate determination process unit for setting said current datatransmission rate to said maximum transmission rate with a probabilityequal to said transmission probability if said desired transmission rateexceeds or is equal to said maximum transmission rate; and a transmitterfor transmitting data to said base unit at said current datatransmission rate.